PROVIDED. Mass spectrometry has become the principal method to identify and characterize proteins and other macromolecular structures that are the functional machinery for biological processes. The purpose of the Mass Spectrometry & Proteomics Facility (MSPF) is to provide Cancer Center members with essential services in macromolecular structural analysis. These services include electrospray and MALDI mass spectrometry for molecular mass determination, tandem mass spectrometry (MSn) for detailed structure analysis (i.e., peptide sequencing), LC/MS/MS analysis for analyzing complex biological mixtures, and database searching for protein identification. The facility has two electrospray ion trap (LC/MS) systems (ThermoElectron LCQ and LTQ) and a high performance MALDI qToF system (PE/Sciex prOTof). The facility is operated both on a fee-for-service and shared use (researchers run their own samples) basis. Facility personnel provide expertise on sample preparation, analysis and data interpretation. They also assist experimental design and the development of novel methodologies. During the most recent 12-month reporting period, the CCMSPF was used by 19 Cancer Center members from all five Research Programs. Peer-reviewed usage represented 72% of total usage. Annual budget for this core is $408,887, of which 69% is institutional funding, 11% is user fees, and 20% ($81,000) is requested from the CCSG.